1. Field of the Invention
This invention relates to a method and a circuit for speech transmission in a broad-band communications network.
2. Description of the Prior Art
A broad-band communications network is known in the prior art (Der Fernmelde-Ingenieur, Volume 41, No. 9, Sept. 1987 ("Switching Technology in Packet Transmission Systems"), pages 2 to 8) wherein signals of different services are transmitted according to an ATD (asynchronous time division) process, i.e., in packets. Transmission of speech signals following dial connections between subscriber's sets is provided in this known system. The broad-band communications network has packing/depacking equipment to form packets and to dissolve them.
In broad-band communications networks in which packets of a fixed length are transmitted, lag times occur in transmission of speech signals due to the required packing/depacking times as well as the processing and waiting times in exchange systems and these lag times can have a negative effect on the quality of speech signal transmissions. For example, if the lag time is too long, it may result in undesirably long speech pauses which interfere with the flow of speech. In addition, connections to subscriber's sets can also take place by way of hybrid sets in broad-band communications networks which include analog/digital telephone switching network in addition to broad-band packet switching networks, and additional problems can occur in a transfer between these networks. Such problems arise from the fact that the transit time of echo signals caused by the hybrid sets can assume a size such that the echo signals are perceived as interference by the telephone subscribers due to the aforementioned lag times in the packet switching networks.
Such echo signals can be suppressed by echo suppressors or echo compensators connected into the transmission lines. However, this requires expensive circuitry which is undesirable in some cases. In addition, there have already been proposals for reducing the lag times in broad-band packet switching networks by filling packets of a fixed length only partially with speech signals in speech signal transmissions.
The problem which the present invention overcomes is reduce the lag times due to the packet switching network in transmission of speech signals at least partially in a packet switching network.